Device for regulating a condition of a main circuit controlled by an auxiliary circuit



Feb. 14, 1939. E w SWANSON 2,146,778

DEVICE FOR REGULATING A CONDITION OF A MAIN CIRCUIT CONTROLLED BY ANAUXILIARY CIRCUIT Filed April 5, 1936 2 Sheets-Sheet 1 I @Wee INVENTOR7676" 50M m JWA/YJO/Y weazw ///J ATTORNEY 2,146,778 CIRCUIT E. W.SWANSON TIN Feb. 14, 1939.

DEVICE FOR REGULA G A CONDITION OF A MAIN CONTROLLED BY AN AUXILIARYCIRCUIT Filed April 5, 1936 2 Sheets-Sheet 2 IN VEN TOR. 5014M 144JW4/X50/y BY W a @140 fl/J ATTORNEY Patented Feb. 14, 1939 UNITED STATESPATENT OFFICE.

A MAIN CIRCUIT CONTROLLED BY AN AUXILIARY CIRCUIT Edwin W. Swanson,Hopkins, Minn., assignor to Electric Machinery Manufacturing Company,

Minneapolis, Minn.

Application April 3, 1936, Serial No. 72,596

18v Claims.

My invention relates to devices for regulating conditions in a mainelectric circuit controlled by an auxiliary circuit and has for anobject to provide a device responsive to the potential and current ofthe main circuit for controlling the current. in said auxiliary electriccircuit.

Another object of the invention resides in providing a device utilizingtwo inductances energized by the potential and current of the maincircuit and acting jointly to control the current in the auxiliarycircuit.

A specific object of the invention resides in providing control meansfor regulating alternating current motors of the synchronous type bycontrolling the direct current excitation to the field winding of thesynchronous motor so as to obtain better motor performance, higherefficiency, greater pull-out torque at heavy loads, and a more uniformpower factor over the entire load range of the motor.

Another object of this invention is to provide a regulating device whichwill cause the motor to produce an instantly responsive increase inmotor pull-out torque to meet any sudden increase in load.

A further object of the invention is to provide a motor and controlsystem which in case of a short circuit on the motor or its connectedelectrical system operates instantly to weaken the main field magneticflux in the motor poles and thereby reduce the generated voltage so asto reduce considerably the magnitude and dura tion of the short-circuitcurrent, which often determines the size and cost of the necessaryswitches and equipment.

Another object of the invention resides in providing a regulating devicefor controlling the power factor of a synchronousmotor, the correctiveeffect of which depends jointly upon" changes in the motor voltage,current, and power factor.

A further object of the invention is to provide a device-simple andeconomical in design, and one which may have no moving parts orcontacts.

A further object of my invention is to provide a regulating device forvarying the direct current excitation to the synchronous motor so as toincrease or decrease the power factor v or to maintain the same constantwith increase of motor load;

An object of the invention is to provide a regulating device forcontrolling the motor field excitation which is automatically andinherently responsive to changes in the motor voltage, the motorcurrent, and/or the motor power factor.

Another object of my invention is to provide a regulating device whichautomatically increases the direct current excitation with increase ofload on the motor so as to hold up the line voltage.

An object of the invention resides in providing a regulating deviceincluding rectifying means for providing field excitation currentwithout the use of the usual direct-current generators.

Another object of the invention is to provide a regulating device havinga magnetic core of three or more legs with inductive windings disposedthereon and connected in such a manner that the flow of flux is in thesame general direction through one of the legs.

An object of the invention is to provide a regulating device whichincludes a regulating winding energized by the resultant flux of twowindings which in turn are energized by the potential and the current ofthe main circuit.

A still further object of the invention resides in providing a method ofprocuring predetermined operating characteristics of a synchronous motorupon variation in loading which consists in varying the excitationcurrent of the field winding of the motor in accordance with the motorpotential, motor current and with or without the power factor.

Another object of the invention resides in providing a method in whichflux components are produced by the motor potential and current, and inwhich regulation is procured by the resultant flux produced thereby.

These, and other objects and advantages of the invention willbe fullyset forth in the following description made in connection with theaccompanying drawings which illustrateseveral modiflcations of myinvention, and in which like reference characters refer to similar partsthroughout the several views.

It will readily become apparent from the following description that theinvention may be put to any number of diiferent uses where amainzbircuit is controlled by an auxiliary circuit. A practicalapplication of the invention is in a synchronous motor circuit and forthe purpose of illustration only such application of the invention hasbeen shown and described. In such application,

Fig. 2 is a view similar to Fig. 1 showing a modification of theinvention. I

Fig. 3 is a view similar to Fig. 1 showing still another modification ofthe invention.

Fig. 4 is a wiring diagram illustrating an embodiment of my inventionfor use with threephase power.

Fig. 5 is a vector diagram. illustrating the relation of the currents,voltages and fluxes in the form of the invention shown in Fig. 4 whenthe motor is operating at unity power factor.

Fig. 6 is a view similar to Fig. 5 illustrating the relation of thecurrents, voltages and fluxes in the form of the invention shown in Fig.4 when the motor is operating at a leading power factor.

Fig. '7 is a wiring diagram illustrating a form of the invention similarto that shown in Fig. 4.

Fig. 8 is a vector diagram illustrating the relation of the currents,voltages and fluxes in the embodiment of the invention shown in Fig. 7.Fig. 9 is a wiring diagram illustrating a modification of the form ofthe invention shown in Fig. 7.

It is well known that where the field excitation of a synchronous motoris fixed and load is then applied upon the motor, the power factordecreases, the armature current increases out of proportion to the load,the efficiency becomes lower, and the motor becomes more subject tostalling due to vinsufiicient torque. In addition when a short circuitoccurs in the power line, the motor acts as a generator and feedscurrent into the short circuit, thereby increasing the magnitude andduration of the short-circuit current. The present invention overcomesall of these objections by varying the field excitation,

current in accordance with the load so that. any

desired performance of the motor can be procured- The structure forproducing these results will now be described in detail.

In Fig. 1 is illustrated at 2| a synchronous electric motor ofsingle-phase type having an armature 22, a squirrel-cage winding ordamping secondary winding 23, and a field winding 24. The motor 2|receives alternating current through leads 25 and 26, which areconnected by means of a switch 21 to a power line P.

' i A direct-current generator 32 is used to supply direct-currentexcitation to the motor field winding 24. This generator comprises anarmature I32 and a shunt field winding 33. The terminals of the armatureI32 of generator 32 are connected through leads 31 and 38 to a fieldswitch 39. This switch is further connected by means of leads I31 andI38 to the field winding 24.

In conjunction with the field winding 24, a field discharge resistance4| is employed which is connected to lead I31 and to an auxiliaryswitching member 40 operable with the switch 39 and connected to leadI38. This resistance prevents injury to the field winding duringstarting.

I The shunt field winding 33 of generator 32 is connected in a shuntfield circuit I33 which is connected to the terminals of the armatureI32. In series with the shunt field winding 33 in circuit I33 is acarbon pile resistor 34 which is operated by a magnetic solenoid 35.This solenoid comprises a winding I35 and a plunger or armature I36adapted to be moved upwardly when the winding I35 is energized. A lever35 is operated by the plunger I36 through a link I00. This lever in turnserves to compress the carbon pile resistor 34 when the solenoid 35 isrespectively of the motor.

actuated, thereby reducing the resistance of said resistor inversely assome function of the current fiowing through winding I35 of saidsolenoid.

My-invention includes a regulating device which I have indicated in itsentirety by the reference numeral 28. This regulating device comprises amagnetic core I3 constructed with three parallel branches or legs I4, I5and IS.

The leg I6 is provided with a current winding 29 which is connected inthe lead 25 to the motor armature 22. This winding receives the entirecurrent fiowing in the armature, though, if desired, only a portion ofthe armature current may be utilized. The leg I5 is provided with apotential winding 3|! and the leg I 6 is likewise provided with apotential winding I30; These windings are connected together by means ofa conductor I; the connection being such that both windings produce fluxin the same direction in the magnetic circuit including legs I5 and It.The windings 35 and I30 are further connected to conductors I9 and I22which in turn are connected to leads 26 and respectively, thussubjecting the windings and |3Il in series to the motor potential. Thecurrent winding 29 is so connected that the resultant flux in leg I5 isgreater than the fiux produced thereby or the flux produced by thewindings 3|! and I30.

The regulating device 23 includes a regulating winding 3| which isconnected to conductors I1 and I8. These conductors are connected to thewinding I of solenoid 35. By means of winding 3|, solenoid 35 isenergized and the position of the plunger I35 is controlled by theamount of current induced in winding 3|.

It is common knowledge that the necessary direct-current excitation toproduce any desired power factor at any load on a synchronous motor isequal to the sum of the field current which compensates for the efiectof magnetic saturation at the internal voltage and the vectorial sum ofthe field current necessary to btain normal voltage on the air-gap lineof the saturation curve on open circuit added at the proper power-factorangle to the field current'necessary to obtain normal armature currenton short circuit.

In the present invention the resultant flux in leg I5 of core I3 isequal to the vectorial sum of the fiux components produced by winding 29and the windings 30 and I30 since these windings are energized by thecurrent and potential Since the flux components produced by the currentand potential of the motor have the same phase angle as the componentsof the excitation current above referred to and since the motor currentvaries with the short-circuit excitation current and the motor potentialvaries with the no-load excitation current, it follows that theresultant flux in leg I5 and the induced voltage in winding 3| varywiththe excitation current required to operate the motor at apredetermined power factor with change of load. It will thus be seenthat if the load on the motor is increased, the motor current increasesand the induced voltage in wind ing 3| correspondingly increases.Likewise; if the power factor in the motor power circuit is changed, acorresponding change in angle between the fiux components in leg I5occurs which produces a corresponding change in the induced voltage inwinding 3|. This increase in induced voltage in winding 3| operates onresistance 34 and produces a corresponding increase in shunt pull-outtorque and efllciency. By the selection of a resistance having theproper characteristics for use as resistor 34, either a leading orlagging power factor can be procured or the power factor may bemaintained at any predetermined value. In a similar manner, compensationmay be had for saturation excitation current.

It will be noted that the response of the motor 2| to the action ofregulating device 28 is subject to the time lag required for building upthe voltage of the generator 32. It is obvious to one skilled in the artthat the essential elements of the regulating device 28 and of resistor34 may be enlarged for greater current capacity so that said resistorcan be connected directly in series with the motor field winding 24. Insuch case direct current excitation may also be obtained from any sourcesuch as a D. C. bus, batteries or manually adjustable generators. Inthis latter form, the time lag for increasing the field excitation isreduced considerably.

In Fig, 2 I have shown a modification of the invention illustrated inFig. 1. Since most of the parts or elements of this form of theinvention are identical with those shown in Fig. l, the descriptionthereof will not be repeatedand the same reference numerals will be usedto designate corresponding parts or elements.

In the form of the invention shown in Fig. 2 the generator 32, resistor34 and solenoid 35 are dispensed with and a bridge rectifier utilizedwhich I have indicated in its entirety by the reference numeral 42. Thisrectifier comprises four rectifying elements I42 which are connectedtogether in the form of a bridge by means of conductors I23, I24, I25and I26. The conductors I24 and I26 are directly connected to conductorsI! and I8 leading from the winding 3|. In a similar manner conductorsI23 and I25 are directly connected to conductors 3,1 and 38, whichsupply direct-current excitation to the motor field winding 24.

In this form of the invention, the winding 3I furnishes the currentwhich is rectified and delivered to the field winding of the motorinstead of controlling the operation-of generator 32 which furnishes theexcitation current in the form of the invention shown in Fig. 1. Sincethe excitation current is derived from winding 3|, regulation isdirectly procured. In this case the'excitation current would be governedby the design of the regulating device 28, which would be designed toproduce the desired operating characteristics for the motor 2I.

In Fig. 2 the current for energizing winding 20 is procured from acurrent transformer 43 which is directly energized by the motor currentthrough lead 26, instead of said winding being directly connected in thepower circuit. Similarly, potential for windings 30 and I30 is procuredfrom a potential transformer 44 which is energized by themotor potentialinstead of said windings being directly connected across leads 25 and 23as in the other form of the invention. This is particularly advantageouswhere the current and voltage are great and where a predeterminedcurrent is to be supplied by winding 3|. It can, however, be readilycomprehended that windings 28, 20 and 3| may be directly connected asshown in Fig. 1 and the regulating device 28 designed accordingly.

The form of the invention shown in Fig. 2 operates in the same manner asthat shown in Fig. 1 to supply excitation current to procure the properoperating characteristics for the same load range as the form of theinvention disclosed in Fig. 1.

In Fig. 3 I have shown a modification of the invention illustrated inFig. 1. In this modification, a thermionic full-wave rectifier 45 isutilized in place of the generator 32 and associated parts of Fig. 1.The thermionic rectifier 45 comprises a cathode 46, and two anodes 48and I48. Anode 48 is connected to the regulating winding 3| by conductorI8 and the other anode I48 is connected to the other terminal oftheregulating winding 3| by conductor II. A center tap 48 of regulatingwinding 3I is connected to a conductor 50 which is connected to thefield switch 39.

The cathode 46 is of the filament type and is heated by external means.For this purpose two heater windings 41, and I" are used, the winding 41being disposed on leg I5 and the winding I" on leg I6. These windingsare connected in series and are connected to the filament 46 by means ofconductors I45 and I46. The filament 46 is connected to the field switch39 by means of a conductor 5|.

The operation of this form of the invention is similar to that of theinvention shown in Fig. 2. The rectifier 45 supplies excitation currentdirectly to the motor field winding 24 and this current is regulated inaccordance with the current, voltage and power factor of the load, toproduce the desired operating characteristics of the motor.

In Fig. 4 I have shown an embodiment of my invention utilizing athree-phase synchronous motor I2I. Since this motor is similar to motor2|, the same reference numerals will be used to designate similar parts,including the field excitation circuit and the switch therein. Motor I2Iis energized by a three phase power circuit 3P which is connected to aswitch I2I. Switch I2'I is connected by means of three leads 52w, 52band 520 to the armature 22 of the motor. A lead 52n is connected to theneutral of the stator winding 22 of motor I2I. The use of this lead willbe subsequently described.

A regulating device I28 shown in the embodiment of Fig. 4 differs fromthe regulating device 28 of Figures 1, 2 and 3 in that it carries threecurrent windings 29m, 291), and 290 on the core leg I4 instead of thesingle winding 28. These windings are connected in series with the leads52a, 52b and 520, respectively, and receive the full current passingthrough the three phases of the motor. The two potential windings 30 andI30 are connected across one phase only, which is accomplished byconnecting lead 52" to winding I30, and by running the conductor I8 connected to winding 30 to the lead 52a. In order to prevent the three fluxcomponents produced by windings 29a, 25b and 29c from neutralizing oneanother, one of there windings is reversed. To cause the fiux componentsof these windings and the flux component of windings 30- and I30 to flowin leg I5 in a manner to make the resultant flux in this leg greaterthan either component,

it is necessary to reverse the current winding' in the lead to which thepotential winding is connected. This would be the winding 29a.

A thermionic rectifier may be used with the regulator I28 if desired.This rectifier would be connected to the regulating winding St, theheater windings 41 and M7, and the switch 39 in identically thesamemanner as the rectifier shown in Fig. 3. For the purpose ofillustration, .two half-wave rectifiers 53 and 54 have been used insteadof a full-wave rectifier. The two anodes es and M3 thereof are connectedto regulating winding 38 and the two filaments 46 and M6 thereof areconnected in parallel to the heater windings ll and Ml.

Fig. 5 is a vector diagram illustrating the relation between thevoltages, currents and iiu.:es in the form of the invention shown inFig. 4. The voltage vectors are designated by the reference character Ewith sufiixes indicating the leads across which the voltages are taken.The

' current vectors are indicated by the reference character I togetherwith similar sufiixes indicating the leads in which the currents flow.The flux vectors are ,indicated by the reference character B with asuffix designating its source. It will thus be seen that Eab representsthe voltage between motor leads 52a and 52b, and Elm represents thevoltage from lead 520. to the neutral lead 521: going to the staror'neutral potential of armature winding 22. For unity power-factoroperation, the motor currents will be in phase with their respectivevoltages to neutral, hence the motor currents may be represented by Ia,Ib and 10. My invention utilizes the voltage Ean for .energizing thepotential windings 30 and I30. Since all three currents are used, thevectorial sum of the same would be zero. To overcome this, one of thewindings, namely winding 29a, is reversed. Thus the vectorial sum of thethree currents-Ia, Ib and I0 is a finite quantity and is represented bythe vector Ir. Since the current windings are reactive, the resultantcurrent Ir, must lag its corresponding voltage ET, by an angle somewhatless than 90 as shown. This voltage Er produces in leg It a fiux Brwhich varies therewith. Similarly Ean produces a fiux' Ban in legs l5and i6, and the amount of this fiux varies with said voltage. Thesefluxes combine in leg IE to produce a resultant fiux Bu that is equal tothe vectorial sum of the aforementioned fluxes.

As hereinbefore explained, unity power-factor excitation of asynchronous motor is approximately equal to the vectorial sum ofthefield excitation current necessary to obtain normal voltage on opencircuit added at 90 to the field excitation current necessary to obtainnormal current on short circuit. Now the fiux Ban due to the potentialwindings 30 and I30 may be compared to the field excitation currentnecessary to obtain normal voltage on open circuit and the flux Br dueto the current windings 29a, 29b and 290, may be compared to the fieldexcitation current necessary to obtain normal fullload current-onshort-circuit conditions and further since the phase angle in bothinstances is substantially 90, it becomes evident that the resultantflux Bu in leg I5 varies in proportion to the necessary field excitationcurrent to maintain unity power-factor operation,from no load to fullload. In order to obtain this characteristic the regulating device 28must be liberally designed so that the operating range lies on thestraight part of the magnetization curve before reaching saturation.Thus at no load, or at full the flux Bu in leg I5 will vary to providethe" tion maintains 80% leading power-factor operation for the samemotor load. The same voltage vectors are present as in Fig. 5 but thevectors of the motor currents have increased about 25% in length(assuming the same load) and the motor currents lead their respectivevoltages by a phase angle whose cosine or powerfactor is 0.80. Since thesame current winding 29a on leg Id is still reversed, its vector isshown as -Ia and the result of the three currents is IT which lags itscorresponding voltage Er, The voltage vector Ean is utilized to energizethe potential windings 30 and I30. Thus in the regulating device 28, theresultant flux B80 will be equal to the vectorial sum of the fluxes Brand Earn due to the voltages Er and Ean respcctively. the necessaryfield excitation current to maintain substantially 80% leadingpower-factor operation from no load to full load. At no load, the motorcurrent is small but suficient so that its effect on the regulatingdevice 28 along with that due to the motor voltage produces a fieldexcitation current which maintains 80% powerfactor operation of themotor IZl. With increase of load, the motor current increases so thatits effect represented by the vector 11' along with that due to themotor voltage produces an increased fiux in leg l5 and thereby producesan increased field excitation current which also maintains 80% leadingpower factor at intermediate and full" loads.

By comparison of Figs. 5 and 6, it will be noted that with the same loadand with more leading power factor, the current vectors increase inlength and the phase angle between said current vectors and. theirrespective voltages become greater. With this increase of phase angle,the angle a between Ean and Er decreases, which results in a greaterflux as shown by B80 It will be noted that with increase of powerfactor,.the voltage vector Er increases in length (assuming the sameload) and the angle a between Ean and Er decreases, both of whichactthrough their respective windings to increase the flux in leg it asshown by the increased vector B80 and thereby furnishes increasedexcitation current to the motor fieldwinding 26. Similarly, withdecrease of power factor, the fiux is decreased as shown by vector Buand the device thereby furnishes reduced excitation current to the motorfield winding 24. It will thus be noted that the amount of flux throughthe leg i5 is a function of the motor voltage, the motor current, andthe motor powerfactor, since this flux varies with each of the threevariables and combinations of the same so as to derive net results whichcompensates for each variable under all conditions. Accordingly, withproper design, the

. power factor can be maintained at a predetermined desired value or canbe controlled so as to resultin a more leading or a more lagging powerfactor with increase of motor load.

In Fig. '7 I have shown a modification of my invention applied to athree-phase synchronous motor 22L In this form of my invention, Iutilize three regulating devices 28a, 28b and 28c. These This fluxvaries in proportion to regulating devices are similar to the regulatingdevice 28 of Fig. 4. The description thereof will hence not be repeatedand the same reference characters will be used to identify the identicalparts. The' reference sufilxes a, b and 0 will be added to thesereference characters to identify the parts of the respective regulatingdevices 28a, 28b and 280. In this form of the invention, the currentwindings 20a, 29b and 290 are disposed on legs Ha, Nb and Me of therespective devices 28a, 28b and 280. These current windings are allreversed and are energized by the respective phase currents of the motorthe same as in the other form of the invention. In addition to thepotential windings 30 and I30 of the other form 01 the invention whichis energized by phase voltage Ean and which are in Fig. 7 designated bythe reference characters 30a and mm, I utilize other potential windings30b, l30b and 300, I 30cwhich are connected across the leads 52b and5211, and across leads 52c and 5211 respectively. These windings aredisposed on the legs l5a, l6a, I55, I61), I50 and "5c of the respectiveregulating devices 28a, 28b and 280.

The three pairs of heater windings 41a and Illa, 41b and lb, and He and1c are connected and energized as in Fig. 4 to furnish the cathodevoltages to the six half-wave rectifiers, 53a and 54a, 53b and 54b, and530 and File. The three regulating windings 3 la, Slb and 3 I0 are alsoconnected and energized as in Fig. 4 to furnish the anode voltages tothe same six respective rectifiers. The direct current output of thesesix rectifiers supplies the direct-current excitation to the motor fieldwinding 24 as previously described. It will be noted that the currentwindings 29a, 29b and 200 are all reversed in this embodiment, and eachregulating device 20a,-

28b and 280 operates in conjunction with its windings thereon and itspair 01 hall-wave rectifiers to produce the necessary direct-currentexcitation to the motor field winding 24.

Since the operation of the form of the invention shown in Fig. 7 issimilar to that shown in F18. 4, the explanation thereof will not berepeated.

Actual tests made with the various forms of my invention show excellentresults. with a 125 H. P. motor and a regulating device such as shown inFig, '7, the motor load was increased from no load to 110% of full load.Throughout this entire load range, the powerfactor varied only threetenths of one percent (0.3%) from unity power factor; and the fieldexcitation current to the motor field winding increased from 7.0 amperesat no load to 10.8 amperes at full load and to 11.2 amperes at of fullload of the motor. Simultaneously, the pull-out torque increased inapproximate direct ratio with the increase of field excitation current.The heating of the motor field winding was considerably reduced at lightloads since the heating varies as the square of the field excitationcurrent. Also, the heating of the motor armature windings was reduced byholding unity power factor. In this test, the core section oi each ofthe three legs of the regulatingdevices was approximately 6.25 squareinches, each current winding had 14 turns; and for 800 volts thepotential windings each had 350 turns, the heater windings each had 4turns, and the regulating windings on the center legs had 240 turns ofcopper wire.

Fig. 8 is a vector diagram illustrating the relation between thevoltages, currentsand fluxes in the form of the invention shown in Fig.7.

In a test made Voltage vectors Ean, Elm and Ecn represent the phasevoltages between the respective power line leads and the neutral point.For unity poweriactor operation, the motor currents are in phase withtheir respective phase voltages to neutral. In this embodiment of myinvention, all phase voltages to neutral and all motor currents areutilized in the regulating devices 28a, 28b and 280.

Each phase voltage and its motor current energize one device whichoperates to control the direct-current output of one pair of half-waverectiflers, Since the current windings 29a, 29b and 29a are reversed andreactive, their currents Ia, Ib, and Ic must lag by nearly 90, theirrespective voltages Ean, Elm and Ecn. Voltages Ean, Ebn and E011. eachproduce fluxes in legs l5a, lib and llic and Ila, lb and lie oi theregulating devices 20a, 28b and 28c and the amount of flux varies withthe corresponding voltage. Similarly, voltages Ear, Ebr and Ecr producein legs a, b and llc fluxes which vary with the motor current of therespective phases of the motor. These current and voltage fluxes combinein leg I! of each of the devices 28a, 20b and No to produce resultantfluxes Ba, ED and Be in each legli that are equal to the vectorial sumsor the aforementioned fluxes.

It will be noted that in the form of the invention shown in Fig. 4, thecurrent windings 20a, 29b and 29c act collectively to produce therequired fiux in regulating device I28 to give the necessary fieldexcitation current, while in the form of the invention shown in Fig. 7,these current windings actindependently, and the direct currentsproduced thereby are combined to produce a resultant current of therequired magnitude. It will become evident, however, that with sixrectifier tubes instead 01. two, more nearly uniform direct-current willbe produced.

In Fig. 9 I have shown a further modification o! my invention for athree-phase synchronous motor 22l utilizing asynchronous converter 51for controlling the direct current excitation to the motor field winding24, This modification of my invention is somewhat similar to that shownin Fig. 7 except that no rectifiers are utilized and consequently noheater windings are required for heating up or energizing the cathodesor filaments of the rectifiers. In this modification, the

induced voltages in regulating windings 31a,

MD and Mo on legs lia, llib and IE0 of the regulating devices 28a, 28band 280 cooperate to supply a three-phase alternating current to thesynchronous converter 51. The voltage of the direct-current output ofthe synchronous converter 51 is controlled by the input voltage of thealternating current which is obtained'irom the induced voltages in theregulating windings am. 3lb and Sic. Thus the induced voltages in theregulating windings directly control the directcurrent output of thesynchronous converter 51 which furnishes the direct current forenergizing the shunt field winding 33 of the generator 32. A rheostat BIis included in the shunt field circuit of the generator 32 so that thedirect-current excitation can be manually adjusted as desired.

The operation from no load up to full load on the motor shown in Fig. 9is similar to that of the prior modifications of my invention in thatthe direct-current excitation to the motor fleld winding increases withload to supply the necessary direct-current excitation to the motorfield winding 24 and thereby maintains substantially the desiredefliciency, pull-out torque and power factor from no-load to full-loadoperation of the motor.

, It will be understood that my invention is not limited to any specifictype of rectifying device since it is obvious that thermionic rectiflersof both the half-wave and full-wave types, mercury arc rectifiers,copper-oxide rectifiers, synchronous converters and the like may beused. It will also be understood that suitable potential and/or currenttransformers may be used on high voltage systems or large currentsystems. To obtain flexibility in the operative characteristics, tapsmay be used on the various windings and variable impedances may beinserted so that the desired characteristics will result.

It will also be understood that the various features of the difierentforms of the invention may be incorporated in any of the modificationsdisclosed, without departing from the spirit of the invention and thatother modifications may be made by combining certain of the elements ofone formwith other elements of other forms of the invention.

My invention besides being applicable to one and three-phase systems asdescribed herein, is obviously applicable to other polyphase systems bysuitable changes which can be readily determined by one skilled in theart.

While theories have been advanced as to operation of the regulatingdevice and methods here described, this has been done with a view tofacilitating the description thereof and it is to be understood that Ido not bind myself to these or any other theories.

The advantages of my invention are as follows: My invention provides asimple, automatic, and instantaneous means of providing over-excitationcurrent which results in increased pull-out torque coincident withincrease of load whether gradually or suddenly increased. Thus asynchronous motor of standard design will be able to successfully carrypeak loads much greater than the maximum peak load the same motor willcarry with constant field excitation current fixed at normal full-loadvalue. Similarly, a synchronous motor especiallydesigned for extremevariations in load such as occur in steel-mill roll drives, may, byusing my invention, be made to successfully carry peak loads muchgreater than (it will carry with constant excitation current fixed atnormal full-load value. In such special drives the size and cost of themotor are largely determined by its capacity to carry peak loads.

1 Thus my invention for increasing the peak-load capacity of anysynchronous motor makes possible the use of a smaller and less expensivemotor for any given application. With my invention, the motor powerfactor can be controlled to give a rising value in the leadingdirection, or a falling value in the lagging direction, or even maintaina constant value-all with increasing load. For best efiiciency,,thepower factor should be maintained at unity for all loads. It will alsobe noted that the efliciency of the motor is increased, the motorheating is decreased, and the operating characteristics of the powerline improved. With my invention where a short circuit occurs in thepower line or motor armature, the motor does not operate as a generatorand hence does not feed current into the short circuit. This is due totwo principal factors. First, the short-circuited current in the currentwindings acts to produce a large flux that will flow through the rightoutside leg instead of through the center leg which carries theregulating winding for supplying 0r arearrs regulating the excitationcurrent to the motor field winding. Second, the voltage across the twopotential windings becomes zero during short circuit so that thesewindings act as a choke coil to rapidly reduce the amount of fluxflowing and thereby operate to rapidly reduce the magnitude of theshort-circuited current. Both factors immediately cooperate toannihilate the excitation current to the motor field winding so that themachine cannot act as a generator to feed current into the shortcircuit. Thus switching equipment of lower capacity may be used inconjunction therewith.

It will, of course, be understood that various changes may be made inthe form, details, proportions and arrangements of the parts, withoutdeparting from the scope of my invention which, generally stated,consists in a device capable of carrying out the objects above set forthand in the novel parts and combination of parts disclosed and defined inthe appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In adevice for regulating a condition of a main electric circuitcontrollable by an auxiliary electric circuit, a magnetic corecomprising three legs in parallel, a potential winding on one of saidlegs, a second potential winding on another of said legs, said windingsbeing connected in series and energized by potential of said maincircuit, a current winding on said third leg and connected in said maincircuit, and a regulating winding on one of said first named legsconnected to said auxiliary circuit.

2. In a device for regulating a condition of a main electric circuitcontrollable by an auxiliary electric circuit, a magnetic corecomprising a plurality of legs in excess of two arranged in parallel,potential windings on a plurality of said legs, said potential windingsbeing connected in series and energized by potential of said circuit, acurrent winding on a leg other than the legs having said potentialwindings, and connected in said main circuit, and a regulating windingon one of said legs having the potential windings, said regulatingwinding being connected to said auxiliary circuit.

3. In a device for regulating a condition in a polyphase electriccircuit controllable by an auxiliary electric circuit, a magnetic corecomprising a plurality of legs in excess of two arranged in parallel,potential windings on a plurality of said legs, said windings beingconnected in series and energized by the potential of one phase of saidpolyphase circuit, a plurality of current windings on another of saidlegs, each of said current windings being energized by the current ofone of said phases of the polyphase circuit, and means energized by themagnetic flux through one of said legs having a potential winding, saidmeans controlling the current in said auxiliary circuit.

4. In a device for regulating a condition of a, mainelectric circuitcontrollable by an auxiliary electric circuit, a magnetic corecomprising a' of said legs, said windings being connected in series andenergized by potential of said main circuit, and being connected so asto produce components of magnetic flux in the same direction in onecertain of said legs, a current winding on said third leg and connectedin said main circuit, said current winding being connected so as toproduce with the fiux produced by said potential winding a resultantmagnetic fiux in said aforementioned certain leg of greater magnitudethan either of said component fluxes and a regulating winding on saidaforementioned certain leg connected to said auxiliary circuit.

6. In combination with a synchronous motor having an armature and afield winding, a regulating device comprisinga magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energized byarmature current, a regulating winding on one of said first named legs,and means controlled by said regulating winding for regulatingexcitation for said field winding. I

7. In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potentiaha current winding on a legother than the legs having said potential windings and energized byarmature current, a regulating winding on one of said first named legs,and means controlled by said regulating winding and including arectifier for supplying and regulating excitation current to said fieldwinding.

8. In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energized byarmature current, a plurality of regulating windings on said first namedlegs, and means controlled by said regulating windings including arectifier energized by certain of said regulating windings, said meanssupplying and regulating excitation current to said field winding. Y

9. In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energized byarmature current, a regulating winding on one of said first named legs,a direct current generator for supplying excitation current for saidsynchronous motor field winding, and means controlled by said regulatingwinding for regulating the-field excitation of said generator.

10; In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energized byarmature current, a plurality of regulating windings on said first namedlegs, a thermionic full wave rectifier for supplying excitation currentfor said field winding, said rectifierhaving a cathode in the form of afilament and anodes, certain of said regulating windings being connectedtosaid filament, and other of said windings being connected to saidanodes, and a field excitation circuit connected to said field windingand energized by said rectifier.

11. An excitation current regulator for a synchronous motor having anarmature and. a field winding, said regulator comprising a magnetic corehaving a plurality of legs in excess of two arranged in parallel,potential windings on a plurality of said legs, said windings beingconnected in series and being adapted for energization by armaturepotential, a current winding on a leg other than the legs having saidpotential windings and adapted for energization by armature current, aregulating winding on one of said first named legs, and field excitationregulating means controlled by said regulating winding.

12. In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature-potential, a current winding on a legother than'the legs having said potential windings and energized byarmature current, a regulating winding on one of said first named legs,a circuit for supplying excitation current to said field winding, arectifier having a cathode and an anode, one side of said regulatingwinding being connected to the anode, said regulating winding beingfurther connected to said excitation circuit, means for connecting thecathode to said excitation circuit, and means for heating said cathode.

13. In combination with a three-phase synchronous motor having anarmature provided with windings connected in star formation and a fieldwinding, a regulating device comprising three transformers, eachtransformer comprising a magnetic core having three legs arranged inparallel, potential windings on two of the legs of each transformer, thepotential windings of each transformer being connected in series andbeing further connected together and to the terminals regulatingwindings being connected to corresponding rectifier anodes and to saidexcitation circuit, said cathodes being connected to said excitationcircuit, and means for heating said cathodes.

14. In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energize ii byarmature current, a regulating winding on one of said first named legs,a circuit for controlling the excitation current to said field winding,a variable resistance in said circuit, motive means for varying saidresistance, and meansenergized by said regulating winding for operatingsaid motive means.

15. In combination with a synchronous motor having an armature and afield winding, a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energized byarmature current, a regulating winding on one of said first named legs,rectifier means for supplying excitation current to said field winding,and means connected to said regulating winding for eneramar're current,a regulating winding on one of said first named legs, a synchronousconverter for controlling the excitation current to said field winding,and a circuit including said regulating winding for energizing saidsynchronous converter.

17. In combination with a synchronous motor having an armature and afield winding,-a regulating device comprising a magnetic core having aplurality of legs in excess of two arranged in parallel, potentialwindings on a plurality of said legs, said windings being connected inseries and energized by armature potential, a current winding on a legother than the legs having said potential windings and energized byarmature current, a regulating winding on one of said first named legs,a direct-current generator including a field winding, rectifier meansfor supplying excitation current to said generator field winding, andmeans controlled by said regulating winding for energizing saidrectifier means.

18. In a device for regulating a condition of a main electric circuitcontrollable by an auxiliary electric circuit, inductive means producingin a portion of a magnetic circuit a magnetic fiux component varyingwith the main circuit potential, other inductive means producing in thesame portion of said magnetic circuit a flux .component varying with themain circuit current, said inductive means being arranged to produce insaid portion of the magnetic circuit a resultant flux of a magnitudegreater than the magnitude of either of said flux components, andregulating means energized by the resultant flux and controlling thecurrent in said auxiliary electric circuit.

EDWIN W. SWANSON.

